A subscriber identification module (SIM) is a well know device in the fields of mobile telephony and data communications. A SIM is an integrated circuit, typically embedded into a SIM card, which securely stores network-specific information used to authenticate and identify subscribers on a network, the network typically corresponding to a mobile/cellular telephone network. The most important information stored includes the International Mobile Subscriber Identity (IMSI), which is used to identify a SIM card with respect to its home network, the SIM's unique international circuit card identifier (ICCID) and an authentication key (Ki) used to identify and authenticate subscribers on mobile devices (such as cellular telephones, tablets and mobile computers).
The IMSI number in turn typically comprises one or more of the following:                a mobile country code (MCC), in terms of which use of the mobile device will be limited to one country;        a mobile network code (MNC), in terms of which use of the mobile device will be limited to a pre-determined network, such as Orange, for example; and        a mobile station (i.e. device) identification number (MSIN) in terms of which use of the mobile device will be limited to one SIM card.        
The IMSI is also used for acquiring other details of the mobile device in a Home Location Register (HLR) or as locally copied in a Visitor Location Register (VLR). The HLR is a central database that contains details of each mobile device subscriber that is authorized to use the GSM core network. Thus, as shown in FIG. 1, when the subscriber home SIM 10 is operating in its home network, it communicates with it related home network HLR 14, via a network station 16 and related network 18.
The VLR is a database of the subscribers who have roamed into the jurisdiction of the MSC (Mobile Switching Center) which it serves. Each base station in the network is served by exactly one VLR, hence a subscriber cannot be present in more than one VLR at a time. The data stored in the VLR has either been received from the HLR, or collected from the mobile device. Whenever a new mobile device is detected in its network, the operator not only creates a new record in its VLR, but it also updates the HLR of the mobile subscriber, informing it of the new location of that mobile device.
The Ki authentication key is a 128-bit value used in authenticating the SIM on a mobile network. Each SIM holds a unique Ki assigned to it by the operator during a personalization process. The Ki is also stored in a database on the network.
The SIM card provides a software function that allows the mobile device to pass data to the SIM card to be signed with the Ki. This, by design, makes usage of the SIM card mandatory unless the Ki can be extracted from the SIM card.
Before describing the typical authentication process, to enable a mobile device to connect to a network, the mobile device, at a high level, comprises a baseband processor to manage the antenna-related functions of the mobile device and a SIM card, with the baseband processor communicating with the network. The SIM card in turn comprises a baseband only component that can communicate with the network via the baseband processor. The SIM card further comprises a memory component. The mobile device further comprises an application layer to run software required to operate the mobile device.
With this in mind, the authentication process comprises the following steps:                1. When the mobile device starts up, the application layer requests a connection from the baseband processor.        2. The baseband processor then requests the mobile device's International Mobile Equipment Identity (IMEI) number, which uniquely identifies the mobile device, from the SIM card, as well as the IMSI, which then gets sent as part of a connection/authentication request to the network. The mobile device may have to pass a PIN to the SIM card before the SIM card will reveal this information.        3. The network searches its database for the incoming IMSI and its associated Ki.        4. The network then generates a Random Number (RAND) based on the predefined and from this it generates an authentication vector 1 (AV1).        5. The network then sends the RAND to the mobile device 1. The mobile device 1 then uses its predefined Ki (which should match the Ki used by the network operator) and the RAND to generate an authentication vector 2 (AV2). The mobile device then passes the AV2 back to the network.        6. The network then compares AV1 and AV2, and if there is a match, mobile device is granted access to the network.        
As briefly touched on above, in order to extend the connectivity service of a mobile device to a location that is different from the home location/network where the service was registered, the mobile device needs to undergo a roaming process. In terms of a conventional roaming process, when the mobile device is turned on or is transferred via a handover to a new or foreign network, this new “visited” network sees the mobile device, notices that it is not registered with its own system, and attempts to identify its home network. The visited network then contacts the home network and requests service information (including whether or not the mobile device should be allowed to roam) about the roaming mobile device using the IMSI number.
If successful, the visited network begins to maintain a temporary subscriber record for the mobile device. Likewise, the home network updates its information to indicate that the mobile device is on the host network so that any information sent to that mobile device can be correctly routed.
In terms of the above, it will be appreciated that the annual revenue of the cellular industry worldwide, with regard to the provision of roaming service, makes roaming very lucrative. In this regard, income generated through roaming charges is incurred by end users making or receiving calls, data or text messages outside of their home network. In some countries networks allow users to roam anywhere in the country and not incur any surcharges for using their mobile devices. In other countries, like Canada, simply leaving the metropolitan area that you reside in can result in roaming charges being incurred. However, in almost all cases leaving the country you reside in will result in excessive roaming charges being incurred.
To address some of the raised in the preceding paragraph, for many years, so-called “dual-IMSI” solutions have been available for mobile operators. These allow subscribers to roam outside of their home network using the roaming agreements of another operator (a so-called sponsor operator). These solutions were initially created to allow startup mobile operators, which did not have any of their own international roaming agreements at launch, to still offer worldwide international roaming coverage to their subscribers, but using the agreements of the sponsor mobile operator.
The dual-IMSI solutions were typically implemented using a SIM card running an application arranged to switch from the home network IMSI to the sponsor's IMSI as soon as the subscriber leaves the home country/network. This switching first occurred manually, by the user selecting a setting in a menu, and later, the solutions were improved to include automatic switching of the IMSI.
In recent years, the focus of these solutions has been less on providing wider roaming coverage, and more on reducing the outbound roaming costs of the home network operator, because the sponsor operator has access to lower outbound roaming rates than the home network operator, either because it handles larger volumes of roaming traffic, or because it benefits from special regulatory frameworks, such as the Eurotariff.
The dual-IMSI solutions typically allow the home network operator to control the behavior and usage of its subscribers from its own home network, regardless of whether the subscriber is roaming using the home IMSI, or the sponsor IMSI. As a consequence, the subscriber also keeps the same MSISDN regardless of which IMSI is being used. This is achieved using elaborate signaling platforms, sometimes called “roaming replicators”, which translate signaling in real-time between the sponsor operator's roaming partners, and the operator's home network, so that the home network does not see any difference when the sponsor's IMSI is in use, compared to when the home IMSI is in use. In other words, the home network operator does not need to perform any changes in its network, does not need to install any additional network equipment, and does need any advanced multi-IMSI capable core/home network elements.
There are several problems with the above mentioned solution when it comes to implementation with a new client operator:
1. The traditional dual-IMSI solution requires the sponsor operator to replace the SIM card of every subscriber whom it wants to use the solution with a new SIM card that contains both the home IMSI provided by the home network operator and the additional IMSI provided by the sponsor operator. Since the SIM card is one of the most critical components in a mobile network, operators are very reluctant to deal and handle existing SIM cards, and replacing them would be logistically challenging. Therefore, most mobile networks implement such solutions either from launch, or only for new SIM cards that are being issued to new subscribers.
2. Because the solution is now being used for cost optimization, rather than expanded roaming coverage, it is no longer sufficient to operate with a single sponsor IMSI. Instead, the notion of a multi-IMSI solution has been introduced, whereby multiple IMSIs from multiple sponsor operators are used according to the region where each sponsor operator has the best costs. This requires a more advanced logic on the SIM card as the most cost effective of the multiple sponsor operator IMSIs must be activated depending on the country to which the subscriber is traveling. Because the roaming conditions of a sponsor network changes over time, a static logic in the SIM card is not sufficient, and an advanced logic, which can be controlled by the supplier of the multi-IMSI solution who manages the various sponsor operators, becomes necessary. This requires significant collaboration between the multi-IMSI solution provider, and the SIM card manufacturer, which often means that the multi-IMSI solution provider has developed a complex application tied to a specific SIM manufacturer, which it requires to use to implement the solution. However, the home network operator has no desire to disclose its secret authentication keys (which must be identical between the SIM card and the home network operator's authentication centre in the home network) to a SIM manufacturer whom it may have no experience working with.
Both of the above problems make it very difficult to implement a multi-IMSI solution into an existing mobile network.
The aim of the invention is therefore to provide a method of and system for providing a multi-IMSI solution in an operating mobile network. In particular, the method of the present invention aims to allow the quick and efficient implementation of a multi-IMSI solution in an operating mobile network, without requiring the home network operator to replace SIM cards, communicate secret authentication keys, or install any equipment into its network.